Semiconductor device with profiled work-function metal gate electrode and method of making

ABSTRACT

The present disclosure provides a semiconductor device with a profiled work-function metal gate electrode. The semiconductor structure includes a metal gate structure formed in an opening of an insulating layer. The metal gate structure includes a gate dielectric layer, a barrier layer, a work-function metal layer between the gate dielectric layer and the barrier layer and a work-function adjustment layer over the barrier layer, wherein the work-function metal has an ordered grain orientation. The present disclosure also provides a method of making a semiconductor device with a profiled work-function metal gate electrode.

RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. Pat.Application 17/385,424, titled “SEMICONDUCTOR DEVICE WITH PROFILEDWORK-FUNCTION METAL GATE ELECTRODE AND METHOD OF MAKING” and filed onJun. 26, 2021,which is a continuation of and claims priority to U.S.Pat. Application 16/914,883, titled “SEMICONDUCTOR DEVICE WITH PROFILEDWORK-FUNCTION METAL GATE ELECTRODE AND METHOD OF MAKING” and filed onJun. 29, 2020, which is a continuation of and claims priority to U.S.Pat. Application 15/450,324, titled “SEMICONDUCTOR DEVICE WITH PROFILEDWORK-FUNCTION METAL GATE ELECTRODE AND METHOD OF MAKING” and filed onMar. 6, 2017, which is a divisional of and claims priority to U.S. Pat.Application 14/096,108, having an amended title of “SEMICONDUCTOR DEVICEWITH METAL GATE STRUCTURE COMPRISING WORK-FUNCTION METAL LAYER ANDWORK-FUNCTION ADJUSTMENT LAYER” and filed on Dec. 4, 2013. U.S. Pat.Applications 17/385,424, 16/914,883, 15/450,324 and 14/096,108 areincorporated herein by reference.

BACKGROUND

Complementary metal-oxide-semiconductor (CMOS) technology is asemiconductor technology used for the manufacture of integrated circuits(ICs). CMOS transistors typically utilize polysilicon as the gateelectrode for both NMOS and PMOS transistors, wherein the polysilicon isdoped with an N-type dopant to form NMOS transistors and doped with aP-type dopant to form PMOS transistors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram illustrating a method for fabricating asemiconductor device with a profiled work-function metal gate electrode,according to some embodiments;

FIGS. 2 to 5 are cross-sectional views of a semiconductor device atvarious stages of fabrication, according to some embodiments;

FIG. 6 is an illustration of a crystal structure of an intermediatework-function metal, according to some embodiments;

FIGS. 7, 8 a, 8 b and 9 are cross-sectional views of a semiconductordevice at various stages of fabrication, according to some embodiments;

FIG. 10 is an illustration of forming a work-function metal layer,according to some embodiments;

FIG. 11 is an illustration of a crystal structure of a work-functionmetal, according to some embodiments;

FIG. 12 is a graphical illustration of an interdiffusion energy barrier,according to some embodiments; and

FIG. 13 is a graphical illustration of a profile in a work-functionmetal gate electrode, according to some embodiments.

DETAILED DESCRIPTION

The claimed subject matter is now described with reference to thedrawings, wherein like reference numerals are generally used to refer tolike elements throughout. In the following description, for purposes ofexplanation, numerous specific details are set forth in order to providean understanding of the claimed subject matter. It is evident, however,that the claimed subject matter can be practiced without these specificdetails. In other instances, structures and devices are illustrated inblock diagram form in order to facilitate describing the claimed subjectmatter.

According to some embodiments, a semiconductor device having a metalgate electrode, as opposed to a doped polysilicon gate electrode, isprovided herein. Some embodiments are illustrated with regard tofabricating a NMOS transistor. However, in some embodiments, a PMOS anda NMOS transistor are fabricated so as to be adjacent to one another,spaced apart or fabricated separately.

Referring to FIG. 1 , illustrated is a flow diagram of a method 100 forfabricating a semiconductor device with a profiled work-function metalgate electrode according to some embodiments. Referring also to FIGS. 2to 5 and 7 to 9 , illustrated are cross-sectional views of asemiconductor device 200 at various stages of fabrication according tosome embodiments, such as according to the method 100 of FIG. 1 . Insome embodiments, part of the semiconductor device 200 is fabricatedwith a CMOS process flow. In some embodiments, additional processes areprovided before, during, and after the method 100 of FIG. 1 . FIG. 2illustrates an embodiment wherein the semiconductor device 200 is shownfollowing a chemical mechanical polishing (CMP) on an interlayerdielectric (ILD) that exposes a dummy poly gate.

At 102, a semiconductor substrate 202 is provided. In some embodiments,the substrate includes a wafer, die formed from a wafer, etc. In someembodiments, the semiconductor substrate 202 is a silicon substrate. Insome embodiments, the substrate 202 is at least one of silicongermanium, gallium arsenic, or other suitable semiconductor materials.In some embodiments, the substrate 202 includes one or more dopedregions, such as at least one of a P-well or N-well. In someembodiments, the substrate 202 includes other features such as a buriedlayer or an epitaxy layer. In some embodiments, the substrate 202 is asemiconductor on an insulator such as silicon on insulator (SOI). Insome embodiments, the semiconductor substrate 202 includes a doped epilayer. In some embodiments, the semiconductor substrate 202 includes asemiconductor layer overlying another semiconductor layer of a differenttype. In some embodiments, the semiconductor substrate 202 is a siliconlayer on a silicon germanium layer.

In some embodiments, the semiconductor device 200 includes an isolationstructure 210 such as a shallow trench isolation (STI) feature formed inthe substrate 202 for isolating an active region 204 of the substrate.In some embodiments, the isolation structure 210 includes a localoxidation of silicon (LOCOS) configuration. In some embodiments, theisolation structure 210 is formed from at least on of silicon oxide,silicon nitride, silicon oxynitride, fluoride-doped silicate (FSG) or alow k dielectric material. In some embodiments, the active region isconfigured as at least one of a NMOS device, such as a nFET 212, or aPMOS device (not shown). In some embodiments, the isolation structure210 isolates the active region of a NMOS device 212 from the activeregion of an adjacent device, such as a PMOS device.

At 104, a dummy gate structure 220 is formed over the substrate 202, thedummy gate structure includes a dummy dielectric 216 and a dummy polygate 218. In some embodiments, the formation of the dummy gate structure220 includes forming various material layers, and etching/patterning thevarious material layers to form a gate structure of the nFET 212 device.

In some embodiments, the dummy dielectric 216 is formed on the substrate202. In some embodiments, the dummy dielectric 216 includes an oxide. Insome embodiments, the dummy dielectric 216 includes a thickness rangingfrom about 10 to about 50 angstrom (A). In some embodiments, the dummypoly gate 218 is a polysilicon. In some embodiments, the dummy poly gate218 is formed over the dummy dielectric 216 by a suitable process, suchas deposition. In some embodiments, the dummy poly gate 218 is formed bya chemical vapor deposition (CVD) process utilizing one or more ofsilane (SiH₄), di-silane (Si₂H₆), or di-clorsilane (SiCl₂H₄). In someembodiments, the dummy poly gate 218 is about 200 to about 2000angstroms thick.

In some embodiments, after formation of the dummy gate structure 220,the semiconductor device 200 undergoes additional CMOS processing toform various features of the nFET 212. In some embodiments,semiconductor device 200 includes doped source/drain regions 225,sidewall or gate spacers 227, silicide features, contact etch stop layer(CESL), and an interlayer dielectric (ILD) 230. In some embodiments, thesidewall spacers 227 are formed before the dummy gate structure 220 isremoved such that the dummy gate structure 220 serves to define thesidewall spacers 227. Thus, when the dummy gate structure is 220 isremoved, the opening 288 is defined between the sidewall spacers 227 andwithin the ILD 230, where the ILD 230 serves as an insulating layer. Insome embodiments, the ILD 230 includes an oxide formed by at least oneof a high aspect ratio process (HARP) or high density plasma (HDP)deposition process. In some embodiments, the deposition of the ILD 230fills in a gap between the semiconductor device 200 and an adjacentsemiconductor device. In some embodiments, the adjacent semiconductordevice is a pFET. In some embodiments, a chemical mechanical polishing(CMP) process is performed on the ILD 230 to planarize the ILD until thedummy poly gate 218 is exposed.

At 106, the dummy dielectric 216 and dummy poly gate 218 are removedthereby forming an opening 288 in the ILD 230 as illustrated in FIG. 3 .In some embodiments, the dummy poly gate 218 and dummy dielectric 216are removed by a dry etch, wet etch, combination dry and wet etch, orother suitable process. In some embodiments, the dummy poly gate 218 anddummy dielectric 216 are removed in a single etching process. In someembodiments, a first wet etch process is used to remove the dummy polygate 218 and a second wet etch process is used to remove the dummydielectric 216. In some embodiments, the second wet etch process isselective so as to remove the dummy dielectric 216 while stopping on thesubstrate 202, thereby forming the opening 288.

At 108, a gate dielectric layer 238 and capping layer 239 are formed toat least partially fill the opening 288, as illustrated in FIG. 4 . Insome embodiments, the gate dielectric layer 238 is formed on the sidewall spacers 227 as well as over the active region 204 of the substrate202. In some embodiments, the gate dielectric layer is a high-kdielectric layer. In some embodiments, the gate dielectric layer 238 isformed by at least one of ALD, CVD, metalorganic CVD (MOCVD), PVD,plasma enhanced CVD (PECVD), plasma enhance ALD (PEALD) or othersuitable techniques. In some embodiments, the gate dielectric layer 238is about 5 to about 20 angstroms thick. In some embodiments, the gatedielectric layer 238 includes a binary or ternary high-k film. In someembodiments, the gate dielectric layer 238 is HfOx. In some embodiments,the gate dielectric layer 238 is at least one of LaO, AlO, ZrO, TiO,Ta₂O₅, Y₂O₃, SrTiO₃ (STO), BaTiO₃ (BTO), BaZrO, HfZrO, HfLaO, HfSiO,LaSiO, AlSiO, HfIaO, HfTiO, (Ba,Sr)TiO₃ (BST), Al₂O₃, Si₃N₄ oroxynitrides. In some embodiments, a post high-k deposition anneal isperformed as part of forming the dielectric layer 238.

In some embodiments, the capping layer 239 is formed over the gatedielectric layer 238. In some embodiments, the capping layer 239includes titanium nitride (TiN) or tantalum nitride (TaN). In someembodiments, the capping layer 239 is about 5 to about 50 angstromsthick. In some embodiments, the capping layer 239 includes Si₃N₄. Insome embodiments, the capping layer 239 functions as a barrier toprotect the gate dielectric layer 238. In some embodiments, the cappinglayer 239 is formed by deposition techniques such as at least one ofALD, PVD or CVD. In some embodiments, the capping layer 239 is optionaland thus is not formed.

In some embodiments, an interfacial layer (not shown) is present betweenthe sidewall spacers 227 and the gate dielectric layer 238. In someembodiments, the interfacial layer includes a silicon oxide (SiO₂) layerhaving a thickness ranging from about 5 to about 20 angstroms. In someembodiments, the interfacial layer includes at least one of HfSiO orSiON formed by at least one of atomic layer deposition (ALD), CVD, PVD,thermal oxidation and nitridation, plasma oxidation or nitridation. Insome embodiments, to form the interfacial layer, an Hf film is formed ona thermal oxide by ALD, CVD, or PVD, and then oxidized by thermal O₂ toform HfSiO. In some embodiments, an Hf film is formed by ALD, CVD, orPVD in a reactive O₂ and H₂O ambient.

At 110, an intermediate work-function metal layer 291 is formed on thecapping layer 239, as illustrated in FIG. 5 . In some embodiments, thecapping layer 239 is optional and thus the intermediate work-functionmetal layer 291 is formed on the gate dielectric layer 238. In someembodiments, the intermediate work-function metal layer 291 is an N-typeor P-type work-function metal. In some embodiments, the intermediatework-function metal layer 291 is titanium aluminide (TiAl). In someembodiments, the intermediate work-function metal layer 291 is TiAl₃. Insome embodiments, the intermediate work-function metal layer 291 is atleast one of nickel aluminide (NiAl) or iron aluminide (FeAl).

In some embodiments, the intermediate work-function metal layer 291 isformed by deposition techniques such as at least one of ALD, CVD or PVDat a temperature above about 200° C. In some embodiments, theintermediate work-function metal layer 291 is deposited at a temperaturebetween about 250 to about 500° C. In some embodiments, the intermediatework-function metal layer 291 is deposited at a temperature betweenabout 300 to400° C. In some embodiments, the metal grain orientation ofthe intermediate work-function metal layer 291 is rallied duringdepositions above 200° C. In some embodiments, the intermediatework-function metal layer 291 is amorphous before deposition andcrystalline after deposition. In some embodiments, the intermediatework-function metal layer 291 is a crystallized metal. In someembodiments, the intermediate work-function metal layer 291 has acrystalline XRD profile. In some embodiments, the intermediatework-function metal is crystalline TiAl and is characterized by a XRDpattern with a peak between about 38.0 to about 40.0 degrees 2 theta. Insome embodiments, the intermediate work-function metal has a (111)oriented plane, as illustrated in FIG. 6 . In some embodiments, the(111) oriented plane of the intermediate work-function metal isstoichiometric and alternates close-packed rows of Ti 604 and Al 606, asillustrated in FIG. 6 . In some embodiments, the intermediatework-function metal layer contains a metal that has a FCC crystalstructure 602, as illustrated in FIG. 6 .

In some embodiments, the intermediate work-function metal layer 291 isat least 10 angstroms thick. In some embodiments, the intermediatework-function metal layer 291 is between about 20 to about 100 angstromsthick. In some embodiments, the intermediate work-function metal layer291 is thicker at the bottom of the opening 288 adjacent the substrate202 than along the sides of the opening 288 adjacent to the sidewallspacers 227. In some embodiments, the intermediate work-function metallayer 291 is about 5 to about 40 angstroms thick along the sides of theopening 288 adjacent the sidewall spacers 227 and about 20 to about 80angstroms thick at the bottom of the opening 288 adjacent the substrate202. In some embodiments, the intermediate work-function metal layer 291is at least 1.5 times thicker at the bottom of the opening 288 than atthe sides of the opening 288.

At 112, a barrier layer 293 is formed over the intermediatework-function metal layer 291, as illustrated in FIG. 7 . In someembodiments, the barrier layer 293 is titanium nitride/tungsten nitride(TiN/WN). In some embodiments, the barrier layer 293 is at least one oftungsten nitride (WN), tantalum nitride (TaN) or ruthenium (Ru). In someembodiments, the barrier layer 293 is a multi-metal layer structure. Insome embodiments, the barrier layer 293 is between about 20 to about 100angstroms thick. In some embodiments, the barrier layer 293 is thinnerat the sidewalls than at the bottom of the opening 288. In someembodiments, the barrier layer 293 is formed by deposition techniquessuch as at least one of ALD, CVD or PVD.

At 114, a work-function adjustment layer 296 is formed to fill in theremainder of the opening 288, as illustrated in FIG. 8 a . In someembodiments, the work-function adjustment layer 296 is a metal. In someembodiments, the work-function adjustment layer 296 is Al. In someembodiments, the work-function adjustment layer 296 is deposited byforming a first Al layer by CVD and then forming a second Al layer byPVD. In some embodiments, the work-function adjustment layer 296includes at least one of Al, tungsten (W), copper (Cu), or othersuitable metal material. In some embodiments, a CMP is performed on thesemiconductor device 200 to remove excess material outside of theopening 288, as illustrated in FIG. 8 b .

At 116, a post thermal anneal 298 is carried out to form a work-functionmetal layer 299, as illustrated in FIG. 9 . In some embodiments, thepost thermal anneal 298 is carried out after back end of line (BEOL)processes have been preformed. Although not illustrated, such BEOLprocesses form, inter alia, at least one of conductive contacts ordielectric layers over the semiconductor device 200. The work-functionmetal layer 299 is formed by the post thermal anneal 298 driving thework-function adjustment layer 296 through the barrier layer 293 tointeract with the intermediate work-function metal layer 291. In someembodiments, the post thermal anneal 298 is preformed at a temperatureabove about 200° C. In some embodiments, the post thermal anneal 298 ispreformed at a temperature ranging from about 300 to about 600° C. Insome embodiments, the post thermal anneal 298 is preformed for about 1minute. According to some embodiments, the semiconductor device 200 thushas a metal gate structure 221 formed in the opening 288 in the ILD 230or insulating layer, where the metal gate structure includes the gatedielectric layer 238, the barrier layer 293, work-function metal layer299, and the work-function adjustment layer 296.

FIG. 10 provides an illustration of an embodiment of the post thermalanneal 298 driving the work-function adjustment layer 296 through thebarrier layer 293 to interact with the intermediate work-function metallayer 291 to form the work-function metal layer 299. In someembodiments, the work-function adjustment layer 296 is Al and theintermediate work-function metal layer 291 is TiAl. In some embodiments,the Al from the work-function adjustment layer 296 diffuses through thebarrier layer 293 and interacts with the intermediate work-functionmetal layer 291 thereby forming a TiAl₃ work-function metal layer 299.

In some embodiments, the work-function metal layer 299 contains acrystalline metal. In some embodiments, the work-function metal layer299 is crystalline TiAl₃. In some embodiments, the work-function metallayer 299 includes at least one of crystalline TiAl or crystallineTiAl₃. In some embodiments, the work-function metal layer 299 has acrystalline XRD profile. In some embodiments, the work-function metallayer 299 contains a crystalline work-function metal that has a D0₂₂crystal structure 610, as show in FIG. 11 .

In some embodiments, crystallized TiAl and TiAl₃ are characterized ashaving a lower interdiffusion energy barrier than amorphous TiAl andTi₃Al. FIG. 12 is a graph 1200 illustrating that a Ti-Al interdiffusionenergy barrier for amorphous TiAl is 267 ev as compared to aninterdiffusion energy barrier for crystalline TiAl which is 118 ev.

In some embodiments, the work-function metal layer 299 is greater than10 angstroms thick. In some embodiments, the work-function metal layer299 is between about 20 to about 100 angstroms thick. In someembodiments, the work-function metal layer 299 is thicker at the bottomof the opening than at the sides of the opening. In some embodiments,the work-function metal layer 299 is at least 1.5 times thicker at thebottom of the opening than it is at the sides of the opening.

In some embodiments, the work-function metal layer 299 has an orderedgrain orientation. In some embodiments, the work-function metal layer299 has an ordered metal grain orientation that provides a uniformthreshold voltage and drain current. In some embodiments, thework-function metal layer 299 has a concave or convex profile 1302, asillustrated in graph 1300 FIG. 13 . In some embodiments, thework-function metal layer 299 has an increased Al concentration at thecenter 1301 and edges 1303 a and 1303 b as illustrated in graph 1300 dueto the diffusion of Al from the work-function adjustment layer 296through the bottom and sidewalls of the barrier layer 293. In someembodiments, the increased Al concentration is due in part to theformation of TiAl₃. In some embodiments, the concave or convex profilelowers a resistance between source and drain extensions of thesemiconductor device 200.

According to aspects of the instant disclosure, a semiconductorstructure is provided. The semiconductor structure comprises a metalgate structure formed in an opening of an insulating layer. The metalgate structure comprises a gate dielectric layer, a barrier layer, awork-function metal layer between the gate dielectric layer and thebarrier layer and a work-function adjustment layer over the barrierlayer. The work-function metal having an ordered grain orientation.

According to aspects of the instant disclosure, a semiconductorstructure is provided. The semiconductor structure comprises a metalgate structure formed in an opening in an insulating layer. The metalgate structure comprises a high-k gate dielectric layer, a barrierlayer, a work-function metal layer between the high-k gate dielectriclayer and the barrier layer, a capping layer between the high-k gatedielectric layer and the work-function metal layer and a work-functionadjustment layer over the barrier layer. The work-function metal havingan ordered grain orientation.

According to aspects of the instant disclosure, a method of fabricatinga semiconductor device is provided. The method comprises forming ahigh-k gate dielectric layer in a first opening of an insulating layer.An intermediate work-function metal layer is formed over the high-k gatedielectric layer at temperature greater than about 200° C. A barrierlayer is formed over the intermediate work-function metal layer. Awork-function adjustment layer is formed over the barrier layer and apost thermal anneal is preformed to convert the intermediatework-function metal layer to a work-function metal layer.

Although the subject matter has been described in language specific tostructural features or methodological acts, it is to be understood thatthe subject matter of the appended claims is not necessarily limited tothe specific features or acts described above. Rather, the specificfeatures and acts described above are disclosed as example forms ofimplementing at least some of the claims.

Various operations of embodiments are provided herein. The order inwhich some or all of the operations are described should not beconstrued as to imply that these operations are necessarily orderdependent. Alternative ordering will be appreciated given the benefit ofthis description. Further, it will be understood that not all operationsare necessarily present in each embodiment provided herein. Also, itwill be understood that not all operations are necessary in someembodiments.

Further, unless specified otherwise, “first,” “second,” or the like arenot intended to imply a temporal aspect, a spatial aspect, an ordering,etc. Rather, such terms are merely used as identifiers, names, etc. forfeatures, elements, items, etc. For example, a first channel and asecond channel generally correspond to channel A and channel B or twodifferent or two identical channels or the same channel.

It will be appreciated that layers, features, elements, etc. depictedherein are illustrated with particular dimensions relative to oneanother, such as structural dimensions or orientations, for purposes ofsimplicity and ease of understanding and that actual dimensions of thesame differ substantially from that illustrated herein, in someembodiments. Additionally, a variety of techniques exist for forming thelayers, regions, features, elements, etc. mentioned herein, such asimplanting techniques, doping techniques, spin-on techniques, sputteringtechniques, growth techniques, such as thermal growth or depositiontechniques such as chemical vapor deposition (CVD), for example.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication are generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Also, at least one of A and B or the like generally means A or Bor both A and B. Furthermore, to the extent that “includes”, “having”,“has”, “with”, or variants thereof are used in either the detaileddescription or the claims, such terms are intended to be inclusive in amanner similar to the term “comprising”.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Thedisclosure includes all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements, resources, etc.), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure. In addition, while aparticular feature of the disclosure may have been disclosed withrespect to only one of several implementations, such feature may becombined with one or more other features of the other implementations asmay be desired and advantageous for any given or particular application.

What is claimed is:
 1. A semiconductor device, comprising: a metal gatestructure, comprising: a gate dielectric layer; and a work-functionmetal layer over the gate dielectric layer, wherein: the work-functionmetal layer comprises at least one of TiAl or TiAl₃, and a concentrationof the at least one of TiAl or TiAl₃ within the work-function metallayer has at least two peaks along a gate length direction of the metalgate structure.
 2. The semiconductor device of claim 1, the metal gatestructure comprising: a barrier layer over the work-function metallayer.
 3. The semiconductor device of claim 1, the metal gate structurecomprising: a work-function adjustment layer over the work-functionmetal layer.
 4. The semiconductor device of claim 3, wherein thework-function adjustment layer comprises a metal.
 5. The semiconductordevice of claim 4, wherein the metal is Aluminum.
 6. The semiconductordevice of claim 1, wherein the concentration of the at least one of TiAlor TiAl₃ within the work-function metal layer has at least three peaksalong a gate length direction of the metal gate structure.
 7. Thesemiconductor device of claim 1, wherein the work-function metal layerhas an ordered grain orientation.
 8. The semiconductor device of claim1, comprising: a capping layer between the gate dielectric layer and thework-function metal layer.
 9. The semiconductor device of claim 1,wherein an interdiffusion energy barrier of the work-function metallayer is no more than 150 eV.
 10. A semiconductor device, comprising: ametal gate structure, comprising: a gate dielectric layer; awork-function metal layer over the gate dielectric layer; awork-function adjustment layer over the work-function metal layer; and abarrier layer between the work-function metal layer and thework-function adjustment layer, wherein the work-function adjustmentlayer fills an area defined by an interior perimeter of the barrierlayer.
 11. The semiconductor device of claim 10, wherein thework-function metal layer comprises a metal.
 12. The semiconductordevice of claim 10, wherein an interdiffusion energy barrier of thework-function metal layer is no more than 150 eV.
 13. The semiconductordevice of claim 10, wherein the work-function metal layer comprises atleast one of TiAl or TiAl₃.
 14. The semiconductor device of claim 10,wherein a concentration of metal within the work-function metal layerhas at least two peaks along a gate length direction of the metal gatestructure.
 15. The semiconductor device of claim 10, wherein aconcentration of metal within the work-function metal layer has at leastthree peaks along a gate length direction of the metal gate structure.16. A semiconductor device, comprising: a metal gate structure,comprising: a work-function metal layer; a barrier layer over thework-function metal layer, wherein an interior perimeter of the barrierlayer defines an area and the barrier layer comprises at least one ofTantalum or Ruthenium; and a work-function adjustment layer over thebarrier layer.
 17. The semiconductor device of claim 16, wherein thework-function adjustment layer fills the area defined by the interiorperimeter of the barrier layer.
 18. The semiconductor device of claim16, wherein the barrier layer is in physical contact with thework-function metal layer and the work-function adjustment layer. 19.The semiconductor device of claim 16, wherein the work-function metallayer comprises at least one of TiAl or TiAl₃.
 20. The semiconductordevice of claim 16, wherein a concentration of metal within thework-function metal layer has at least two peaks along a gate lengthdirection of the metal gate structure.